1500
Organometallics 1990, 9, 1500-1508
C,H,( CO),Fe-ql-homoallylidene to C,H,( CO),Fe-q'-all ylidene Rearrangement, a New Route to Vinylmethylidenes via Ligand Rearrangement. Synthesis and 1,4-Additions to (C,H,(CO),Fe-q'-[ 2-( bicycle[ 3.2.1]oct-3-enylidene)]j+CF3S03Robert S. Bly' and Muthukrishna Raja Department of Chemistry, University of South Carolina, Columbia, South Carolina 29208 Received September 28, 1989
An epimeric mixture of [q1-(l-bicyclo[2.2.1]hept-2-enyl)methoxymethyl]C5H5(C0)2Fe, 4 and 5, was prepared by sequential treatment of l-bicyclo[2.2.l]hept-2-enecarbonylchloride with sodium dicarbonyl(~5-cyclopentadienyl)ferrate, methyl triflate, and sodium borohydride in basic methanol. Treatment of 4 and 5 in methylene chloride at -78 "C with fluoroboric acid/diethyl ether or with trimethylsilyl triflate yields C5H5(C0)2Fe-q'-(2-bicyclo[3.2.1]oct-3-enylidene)tetrafluoroborate or triflate, 9+BF4-or 9+Tf0-, intermediate respectively. Attempts to detect the putative ~1-l-(bicyclo[2.2.1]hept-2-enyl)methylidene '6 by monitoring the conversion of 4 and 5 to 9+ at -78 "C by 'H and/or 13C NMR were unsuccessful. This iron(I1) homoallylidene to allylidene rearrangement constitutes a new route to @,y-unsaturatediron(I1) methylidenes. Molecular mechanics calculations (PCMODEL/MMX)employing metallic carbocations as models for the iron(I1) methylidenes are utilized to predict the course and relative facility of the rearrangement. A variety of nucleophiles (Nu),viz., lithium triethylborohydride, methyllithium, methyllithium in the presence of Cu(1) or Ce(III), lithium dimethylcuprate, dilithium dimethylcyanocuprate, methanol/NaHC03, p methylthiophenoxide, dimethyl lithiomalonate, and vinyllithium react stereoselectively with 9+ a t the y-position to yield a single complex, 10-15, respectively, in each case. Addition is exo with methyllithium, lithium dimethylcuprate, and dilithium dimethylcyanocuprate and is presumed to be so with methanol/sodium bicarbonate, dimethyl sodiomalonate, and vinyllithium as well. When protonated with trifluoroacetic acid in methylene chloride a t -78 "C, both 10 (Nu = H)and l l (Nu = Me) yield C5H5(CO)2Fe-exo-q2-(e~o-4-Nu-bicyclo[3.2.l]oct-2-ene) trifluoroacetates, 9+ (Nu = H) and 19+CF3C02-(Nu = Me), respectively, which rearrange when warmed above -40 "C to C5H5(CO)2Fe[exo-~2-(4-Nu-bicyclo[3.2.l]oct-2-ene)], 21+CF3C02-(Nu = H), or exo-4-Nu-bicyclo[3.2.l]oct-2-ene, 22 (Nu = Me), respectively. Methyl triflate alkylates 10 (Nu = H)at the &position to form a new alkylidene (q1-2-(3-methylbicyclo[3.2.l]octylidenyl)dicarbonyl(q5-cyclopentadieneyl)irontriflate?), which rearranges and dissociates-3methylbicyclo[3.2.1]oct-2-ene(23) is the final product. Two routes have been used for the synthesis of iron(I1) highly strained, as is an "unstablen4 bridgehead olefin for a allylidenes: protonation of C5H5(CO)(L)Fe-q1-(dienyl) example, further bond migrations can O C C Uforming ~,~ complexes, L = CO or P(OCHJ3,' eq 1, a n d protonation new, rearranged alkylidene, eq 4. If the original C5H5of a C5H5(CO)2Fe-~1-4-(2-methyl-3-buten-2-ol),2 (CO),Fe-neopentylidene were to contain a homoallylic eq 2. double bond, its rearrangement could produce a C5H,TlOH Fp'+ TfO' (1) (CO)2Fe-allylidene, eq 5. F P * W
CWt, -60 to -20%
FP'. Cp(CO)[P(OMe)p]Fe
Fp= Cp(CO)>Fe
We have recently shown that protonation of C5H5(CO)2Fe-a-alkoxyneopentyl-type complexes produces which rearrange to cationic C5H5(CO)2Fe-neopentylidenes q2-olefin ~ o m p l e x e s eq , ~ 3. If the complexed alkene is Me Fp'dH-C-Me
I
I Me
-
To test this possibility a n d hopefully to extend the original rearrangement t o include functionally substituted derivatives, we have investigated t h e synthesis a n d rearrangement of t h e u n s a t u r a t e d methylidene [C5H5(CO)2Fe-q2-(l-bicyclo[2.2.l]hept-2-enyl)methylidene]+(6'). We now report the results of our study which include a new method for the formation of cationic, C5H5(C0)2Fe[ q1-(3-allylidenes)],ls2 i.e., vinylmethylidenes, by rearr a n g e m e n t of cationic, C5H5(CO),Fe[q1-(4-homoallylidenes)], i.e. 3-allylmethylidenes, as well as some nucleophilic and electrophilic additions to this relatively new b u t potentially useful functionality.
Fp+MxMe (3)
H
Me
Results After some initial difficulties6 t h e requisite [ql-(l-bicy-
(1) Kuo, G.-H.; Helquist, P.; Kerber, R. C. Organometallics 1984, 3, 806. (2) (a) Casey, C. P.; Miles, W. H. Organometallics 1984, 3, 808. (b) Casey, C. P.; Miles, W. F.; Tukada, H. J. Am. Chem. SOC.1985,107,2974.
(3) (a) Bly, R. S.; Bly, R. K. J . Chem. SOC.,Chem. Commun. 1986, 1046. (b) Bly, R. S.; Hossain, M. M.; Lebioda, L.; Raja, M. J.Am. Chem. SOC.1988, 110, 1723. (4) Maier, W. F.; Schleyer, P. von R. J . Am. Chem. SOC.1981, 103, 1891. ( 5 ) Bly, R. S.; Silverman, G. S.; Bly, R. K. J.Am. Chem. SOC.1988,110, 7731.
0276-7333/90/2309-1500$02.50/00 1990 American Chemical Society
New Route to Vinylmethylidenes
Organometallics, Vol. 9,No. 5, 1990 1501 Scheme I11
Scheme I
1
2
3' i
" N a F p or KFp, T H F , 25 "C. MeOTf, CH2C12, 25 OC. BHEt,, THF, CHpClp, -78 t o +20 OC.
FpOCOCF3
Na-
Scheme I1
A
/ - &$
LL
H /
\
FP 4, 5 a)
6' HBF,, E120
b)
9* BF4- or TfO'
TtOSiMe,
clo[2.2.1]hept-2-enyl)methoxymethyl]C5H5(CO)zFe was prepared as a -3:2 mixture of diastereomers 4 and 5 from the known l-bicyclo[2.2.l]hept-2-enecarbonylchloride7 (1) as outlined in Scheme I. Treatment of a mixture of 4 and 5 in methylene chloride a t -78 "C with fluoroboric acidldiethyl ether8q9 or with trimethylsilyl triflate'O yields C5H5(CO)zFe[.r11-(2-bicyclo[3.2.l]oct-3-enylidene)] tetrafluoroborate or triflate, 9+BF; or 9+Tf0-, respectively, Scheme 11. Attempts to detect the putative .r11-[l-(bicyclo[2.2.1]hept-2-enyl)methylidene] intermediate 6' by monitoring the conversion of 4 and 5 to 9+ a t -78 "C by lH and by 13C N M R were unsuccessful. Although the rearranged, &yunsaturated alkylidene 9+Tf0- can be isolated as a yellow precipitate when the cold (-78 "C) reaction mixture is diluted with diethyl ether, it too is apparently unstable above about -20 0C.293,5 Allylidene 9+Tf0- adds a variety of nucleophiles a t reduced temperature, a single product being formed in each case. T h e regiochemistry of the addition follows from the resonance a t b 157-146, which appears in the 13C NMR spectrum of each product, corresponds t o a "quaternary" carbon (INEPT"), and is attributable to (C5H5(C0)zFeC(-)=)+.2bJ2 T h u s 9+ is attacked by nucleophiles a t the "y-position", C(4), forming "1,4-addition" products, viz., 10-15, exclusively, Scheme 111. In no case was any "1,2addition" product observed.
(6)Our early attempts to prepare pure 3+Tf0- were frustrated by the quixotic formation of varying amounts of a saturated, polycyclic Fischer carbene of fairly high local symmetry which could not be separated from 3+Tf0-by fractional crystallization. We were able later to identify this material as dicarbonyl($-cyclopentadienyl) [q'-(1-nortricycly1)methoxymethylideneliron triflate. Its identification, separate preparation, and reactions will be reported subsequently. (7) Wilt, J. W.; Parsons, C. F.;Schneider, C. A.; Schultenover, D. G.; Wagner, S. J.; Wagner, W. J. J. Org. Chem. 1969,33,694. (8) Jolly, P.W.; Pettit, R. J. Am. Chem. SOC.1966,88, 5044. (9)Green, M. L.H.; Ishaq, M.; Whitley, R. N. J. Chen. SOC.A 1967, 1508. (10)Brookhart, M.; Tucker, J. R.; Husk, G. R. J.Am. Chem. SOC.1981, 103,979. (11) These assignments are supported by refocused INEPT (cf.: Morris, G. A.; Freeman, R. J. Am. Chem. SOC.1979,101,760), a routine made available to us by our colleague Dr. Ron Garber. (12)(a) Reger, D. L.; Coleman, C. J.; McElligot, P. J. J. Organomet. Chem. 1979,171,73.(b) Reger, D.L.; Coleman, C. J. I n o g . Chem. 1979, 18, 3156. (c) Reger, D.L.; Belmore, K. A.; Mintz, E.; McElligot, P. J. Organometallics 1984,3, 134. (d) Reger, D. L.; Swift, C. A. Organometallics 1984,3,876. (e) Reger, D. L.; Belmore, K. A. Organometallics 1985,4 , 305.
\
\ e
14
fP
&H=cH2
15
FP
"LiHBEt3. MeLi. Li2Me2CuCN. MeLi, Cu(I), or Ce(II1). MeOH/NaHCO, f HBF,, Et2O. 8 p-MeC6H,S-. LiCH(CO,Me),. LiCH=CH2. CF3C02H, CH2C12,-78 O C . J
Attempts to induce "1,2-addition" to 9+Tf0- were unsuccessful. With methyllithium in the presence of Ce(III)13 a t -78 "C 11 was the only addition product detected. Triphenylphosphine and trimethyl phosphite, which attack the a-position of simple Fe(I1) alkylidenes and of the P,y-unsaturated alkylidene [ (CO)(a5-C5H5)[P(OCH,),]Fe= CH-CH=C(CH3)2]+BF4- to form stable phosphonium ~ a l t 5 , ' 8 ~ J eqs ~ 6 and 7, may add to the methylidene carbon,
C(2) of 9+ a t reduced temperature, but the products are apparently unstable and revert to starting material, which decomposes when warmed to room temperature. T h e stereochemistry of nucleophilic 1,li-addition t o 9+TfO- is expected to be exo for this is the kinetically preferred pathway of both electrophilic addition to bicyclo[3.2.1]0ct-2-enes'~and 1,4-nucleophilic addition t o bicyclo[3.2.1]0ct-2-en-4-one,~~J~ eq 8. Both methyllithium and
dilithium dimethy1cyanocupratel8 react in this manner: (13)(a) Imamoto, T.; Kusumoto, T.; Tawarayama, Y.; Sugiura, Y.; Mita, T.; Hatanaka, Y.; Yokoyama, M. J. Org. Chem. 1984,49,3904.(b) Imamoto, T.; Takiyama, N.; Nakamura, K. Tetrahedron Lett. 1985,26, 4763. (14)(a) Bodnar, T.; Cutler, A. R. J. Organomet. Chem. 1981,231,C31. (b) Bodnar, T. W.; Cutler, A. R. Organometallics 1985,4 , 1558. (15)Sauers, R.R.;How, H. M.; Feilich, H. Tetrahedron 1965,21,983. (16)Cheminat, B. C.R. Acad. Sci. 1975,28OC,393. (17)Goering, H.L.;Kantner, S. S. J. Org. Chem. 1981,46,4605.
1502 Organometallics, Vol. 9, No. 5, 1990
Bly and Raja
Scheme IV
/ 17'CF3CO2
R=H
CF3C02-(21+CF3C02-),is unstable above -0 "C and decomposes to the free olefin, exo-4-methylbicyclo[3.2.1]oct-2-ene (22), when allowed t o warm t o ambient temperature (Scheme IV). Not ~ u r p r i s i n g l y ,12 ~ ~reacts ~ ~ ~ with HBF4-Et20a t -78 "C to reform 9+BF4-, thus rendering the 1,4-addition of methoxide formally reversible (Scheme 111). Alkylating agents have been shown to react with Fe(I1) and other neutral, late-transition-metal vinyl's a t the "@p o ~ i t i o n " , ' ~ eqs ~ , ~10 ' ~ and ~ ~ 11. Thus methyl triflate reacts
"',,
Me
' \ 10 R=H
16*CF3C0,
R=H
11 R=Me
19'CF3C0,
R=Me
CW),
F~"-CH< ,,'
MeOTl
R=Me
~
Fp"' C(5,6,7)H,'s); 13C(lHJ NMR (CDC13)6 260.55 (>C=O), 214.68, 214.45 (CCH,'s). Anal. Calcd. for CI5H1,FeO3: C, 60.43;, H, 4.73; 0, 16.10. C, 60.29; H , 4.77; 0, 16.28. Preparation of [$-( l-Bicyclo[2.2.l]hept-2-enyl)methoxymethylidene]dicarbonyl(~5-cyclopentadienyl)iron(11) Triflate, 3+Tf0-. To a solution of 0.325 g (1.09 mmol) of 2 in 3 mL of CH,C12 was added 1.00 mL (1.45 g, 8.84 mmol) of methyl trifluoromethanesulfonate (MeOTf), and the resulting solution was stirred at room temperature for 13 h. The reaction mixture was diluted with 40 mL of freshly distilled Et,O to precipitate (38) We thank: (a) Easley Wallace, M.S. Thesis, University of South Carolina, 1978,and (b) Gary Silverman, Ph.D. Dissertation, University of South Carolina, 1984,for earlier preparations of this compound. (39)Cf.: King, R.B. J. Am. Chem. SOC.1963,85, 1918. (40)Wilkinson, G.;Piper, T. S. J. Inorg. Nucl. Chem. 1956,3, 104.
Organometallics, Vol. 9, No. 5, 1990 1505
New Route to Vinylmethylidenes the desired complex 3+Tf0- as a yellow, apparently hydroscopic, microcrystallinesolid, which was further purified by two sequential precipitations from CH2C12/Et,0. The precipitate was dried at reduced pressure to yield 0.395 g (78%),mp 97-98 "C, of 3+Tf0-, which has the following spectral properties: IR (CH,Cl,) 2050, 2005 cm-' ( - C 4 ) ; 'H NMR (CD,Cl,) 6 6.28 (m, 1 H, H(3)),6.17 (d, J = 5.6 Hz, 1 H, H(2)), 5.45 (s, 5 H, Cp H's), 5.01 (s, 3 H, OCH,), 3.09 (br s, 1 H, H(4)), 2.05-1.14 (m, 6 H, >C(5,6,7)H2's); 208.57 %l1H} NMR (CD,Cl,) 6 343.91 ((C5H5)(CO),Fe=C(R)~), ( - C ~ S ) ,137.71and 133.94 (CH=CH), 88.03 (Cp), 83.99 (>CCHP(s). Anal. Calcd for C17Hl,F3Fe06S: C, 44.17; H, 3.71. Found:43 C, 40.62 f 3.55; H, 3.84 f 0.13. FAB MS, m/e for [MI'+ (Cl6Hl7FeO3S) calcd 313.0557, found 313.0527, [M - CO]" (C15H17Fe02) calcd 285.0605, found 285.0578. Preparation of [q'-( l-Bicyclo[2.2.l]hept-2-enyl)methoxymethyl]dicarbonyl($-cyclopentadienyl)iron(II) as a Mixture of Epimers, 4 and 5. To a solution of 0.175 g (0.379 mmol) of 3+Tf0- in 5 mL of CH,C12 was added slowly 0.5 mL of a 1 M solution of LiBHEt, in THF. The reaction mixture was stirred at -78 "C for 10 min and then allowed to warm to ambient temperature as the volatiles were removed at reduced pressure. The resulting residue was extracted with 3 x 10 mL of 1O:l pentane/diethyl ether and filtered through a short column of alumina to provide a clear yellow filtrate, which upon concentration at reduced pressure yielded a yellow solid. This residue was dissolved in a minimum volume of hexane and chromatographed on alumina at -10 "C using hexane as eluant. Both diastereomers, i.e., 4 and 5 , were eluted as a single yellow band by using 19:l hexane/diethyl ether. The isolated yield after purification was 0.105 g (88%). The composition of the diastereomeric mixture was determined to be -62:38 by 13C(1HJ NMR, vide infra, but no attempt was made either to determine the stereochemistry of or to separate the individual components. The mixture of 4 and 5 has the following spectral properties: IR (CH2C12)1992,1932 cm-l (-CEO); 'H NMR (CD,Cl,) 6 6.07 (m, 2 H, CH=), 4.89 (s, 5 H, Cp H's), 3.30 (s, 3 H, OCH,), 2.79 (br s, 1 H, X H ) , 1.86-1.02 (m, 6 H, >CH2's); 13C('HJNMR (CDzClz)the major epimer, 6 218.50, 216.52 (-C=O's), 137.08 (CH=),133.56 (CH=),85.69 (Cp),86.40 (FeCH(0)-),67.38 (>CCH2),41.63 (>CH), 33.25 and 27.79 (>CH2's), the minor epimer, 6 218.50, 216.52 (-CEO'~), 137.66 (CH=),134.05 (CH=),85.84 (Cp), 84.18 (FeCH(0)-),67.57 (>CCH,), 41.63 (+CH), 29.23 and 27.18 (>CH,'s); mass spectrum, m/e 314 [MI'+, 286 [M - CO]", 258 [M - 2CO]'+. Anal. Calcd for C16H18Fe03: C, 61.15; H, 5.78. Found:,& C, 60.98; H, 5.65. Formation and Spectral Characterization of [q1-2-Bicyclo[ 3.2.l]oct-3-enylidene]dicarbonyl(q5-cyclopentadieny1)iron(I1) Tetrafluoroborate, 9+BF4-. To a cold (-78 "C), nitrogen-blanketed solution of 0.045 g (0.143 mmol) of 4 and 5 (-62:38) in 0.6 mL of CD,Cl, in a 5-mm NMR tube was added 0.05 mL of cold (-78 "C) HBF4.Eh0. After the contents had been mixed at -78 "C, the cold tube was placed in the precooled (-78 "C) probe of an NR-80 spectrometer, and the l3Cl1HJNMR spectrum was recorded: b 352.48 (C5H5(C0)2Fe+=CCH,'s); l3C(lH)NMR (CD,Cl,) 6 217.44, 147.25 (-C(C5H5(CO),Fe)=), 132.33 (CH=), 217.27 (-C=O's), 85.80 (Cp), 53.59, 34.09 (+CH's), 42.73, 38.08, 33.78 and 31.21 (>CH,'s); mass spectrum, m/e 284 [MI'+, 256 [M - CO]", 228 [M - 2CO]". Anal. Calcd for Cl5Hl6FeO2: C, 63.41; H, 5.68. Found: C, 63.47; H, 5.64. Reaction of [q'-2-Bicyclo[3.2.1]oct-3-enylidene]dicarbonyl(q5-cyclopentadienyl)iron(II)Triflate, 9+Tf0-, and Methyllithium. P r e p a r a t i o n of [q1-2-(exo-4-Methylbicyclo[3.2.l]oct-2-enyl)]dicarbonyl( q5-cyclopentadienyl)iron(II), 11. Cold, precipitated 9+Tf0-, prepared as before from 0.092 g (0.293 mmol) of 4 and 5 and 0.15 mL (0.173 g, 0.776 mmol) of trimethylsilyl triflate, was suspended in 15 mL of cold diethyl ether, stirred at -78 "C for 1 h, and then treated with 0.2 mL of 1.5 M methyllithium in diethyl ether. The suspension dissolved immediately to give a clear, yellow-orange solution, which was stirred at -78 "C for an additional 30 min. The cooling bath was removed and the solution was concentrated to dryness under vacuum as it warmed to room temperature. The resulting residue was extracted with 209 pentane/diethyl ether and filtered through a short column of alumina. Concentration of the filtrate at reduced pressure gave 0.054 g (62%) of the CSH5(CO),Fe-vinylcomplex 11 as a yellow oil: IR (CH,Cl,) 2000,1947 cm-' (-€a); 'H NMR (CDC13) 6 5.07 (d, J = 4.7 Hz, 1 H, =CHCH(CHJ), 4.81 (s, 5 H, Cp H's), 2.38 (m, 1 H, >CHMe), 2.12-0.83 (m, 8 H, 3 >CH2's + 2 X H ' s including a multiplet at 1.85 ppm due to =CHCH(CH3) which, when the doublet at 5.07 ppm is irradiated, is converted into quintet (doublet of a triplet?) and when the doublet at 0.91 ppm is irradiated, is converted into a quarter (doublet of a doublet), 0.91 (d, J = 6.9 Hz, 3 H, CH,); 13C('H)NMR 6 217.33, 216.99 (-C=O's), 146.74 (-C(C5HS(CO)2Fe)=),138.47 (CH=), 85.71 (Cp), 53.60, 45.98, 39.52 (SCH's), 33.31, 32.03, 31.00 (>CH,'s), 21.46 (CH,); MS, [MI'+ cald for Cl6Hl8FeO2298.0656, found 298.0642. Anal. Calcd for Cl6Hl8FeO2:C, 64.43; H, 6.09. Found: C, 62.57 f 0.26; H, 5.97 & 0.03. Reaction of [q1-2-Bicyclo[3.2.1]oct-3-enylidene]dicarbonyl(q5-cyclopentadienyl)iron( 11) Triflate, 9+Tf0-, and Methyllithium i n t h e Presence of Cerous Chloride. An Attempt To Induce l,2-Addition. Cold, precipitated 9+Tf0-, prepared as before from 0.115 g (0.366 mmol) of 4 and 5 and 0.2 mL (1.034 mmol) of trimethylsilyl triflate, was suspended in 20 mL of cold diethyl ether at -78 "C. A clear, greenish yellow solution formed as a cold (-78 "C) solution of methyllithium/ Ce(II1) in THF, prepared as outlined'3b from 0.34 g (1.40 mmol) of anhydrous13bCeC1, and 1.4 mL of -1 M CH3Li (-1.40 mmol) in 20 mL of THF at -20 "C, was added by cannula. The cooling bath was removed after 10 min, and the solution was allowed to
-
1506 Organometallics, Vol. 9, No. 5, 1990
Bly a n d Raja
short column of alumina to give a filtrate, which when concenwarm slowly to room temperature, filtered through a short column of alumina, and concentrated under vacuum to produce a residue, trated at reduced pressure provided a residue that when dissolved in 5 mL of pentane and held overnight at -78 "C yielded 0.118 which was dissolved in pentane and chromatographed on alumina g (87%) of yellow, crystalline 13,mp 68-69 "C: IR (CH,Cl,) 2005, using 1O:l pentane/Et20. The eluted yellow band was concen1955 cm-' (-C=O); 'H NMR (CD2C12)6 7.19 (m, 4 H, Ar H's), trated to yield 0.075 g (0.25 mmol, 69%) of a yellow oil whose 13CNMR is identical with that of [q1-2-(4-methylbicyclo[3.2.1]- 5.28 (d, J = 2.6 Hz, 1 H, CH=CH(SAr), which when the triplet oct-2-enyl)]dicarbonyl(~5-cyclopentadienyl)iron(II), 11. at 3.60 ppm is irradiated is converted into a singlet), 4.83 (s, 5 H, Cp H's), 3.60 (br t, J N 2.7 Hz, 1 H, CH=CH(SAr), which Reaction of [q1-2-Bicyclo[3.2.l]oct-3-enylidene]diwhen the doublet a t 5.28 ppm is irradiated is converted into a carbonyl(q5-cyclopentadienyl)iron(II)Triflate,9+TfO-, and doublet, J = 1.7 Hz), 2.53-0.88 (m, 8 H, 2 >CH's + 3 >CHz's), Dilithium Dimethylcyanocuprate. A n Alternate Prepara2.31 (s, 3 H, CH3) [PCMODELzsb predicts J H ( ~ )=- H 0.76 ( ~HZ, ) tion of [q1-2-(exo-4-Methy1bicyc1o[3.2.1]oct-%-eny1)]diJH(3bH(4) = 3.54 HZ for the ex0 isomer, J H ( 4 ) 4 ( 5 ) = 3.32 HZ, JH(3)4(4) carbonyl(~5-cyclopentadienyl)iron(II),11. Cold, precipitated = 2.97 Hz for the endo isomer]; 13C('HJNMR (CD,Cl,) 6 216.74 9+Tf0-, prepared as before from 0.152 g (0.484 mmol) of 4 and (-C=O's), 157.01 (-C(C5H5(CO),Fe)=), 136.42, 133.31(>C='s), 5 and 0.30 mL (0.345 g, 1.55 mmol) of trimethylsilyl triflate, was 131.45, 129.63 (Ar CH='s), 130.50 (CH=), 86.03 (Cp), 58.14, 54.27 suspended in 10 mL of cold diethyl ether and treated with 25 mL and 39.04 (>CH's), 34.99, 32.46 and 29.58 (>CHz's), 20.99 (CH3); of a cold (-78 "C) solution containing 0.581 mmol of 'Li,Cu378 [M - CO]", 350 [M - 2COI". mass spectrum, m/e 406 [MI'+, (CH,),CN", which had been prepared at -0 "C by adding 2 mol Anal. Calcd for CnH2,Fe02S: C, 65.03; H, 5.46. Found: C, 65.12; equiv of methyllithium in diethyl ether to a slurry of 0.052 g (0.581 H, 5.46. mmol) of cuprous cyanide in diethyl ether.ls The reaction mixture Reaction of [ql-2-Bicyclo[3.2.1]oct-3-enylidene]diwas stirred at -78 "C for 10 min, and the cooling bath was then carbonyl(q5-cyclopentadienyl)iron(II) Triflate,9+TfO-,and removed to allow the temperature of the mixture to rise gradually Dimethyl Lithiomalonate. Preparation of 1q1-2-[4-(Dito room temperature. After 30 min the reaction mixture was carbomethoxymethyl)bicyclo[ 3.2.l]oct-2-enyl]Jdicarbonylfiltered through a short column of alumina, and the resulting (q5-cyclopentadienyI)iron(II), 14. Cold 9+Tf0-, prepared from filtrate was concentrated to dryness at reduced pressure. Further 0.135 g (0.430 mmol) of 4 and 5 and 0.27 mL (0.311 g, 1.40 mmol) purification of the resulting yellow oil was achieved by placing of trimethylsilyl triflate as described above, was suspended in 20 it on a short column of alumina with a minimum volume of mL of cold (-78 "C) diethyl ether. To this slurry was added 5 pentane and eluting with a pentane/diethyl ether mixture. mL of a cold ethereal solution containing 1.5 equiv of LiCHConcentration of the resulting clear yellow solution at reduced (C02Me), (previously prepared at -0 "C by taking 1 equiv of pressure yielded 0.132 g (92%) of the methyl adduct, 11, whose n-BuLi in Et,O to an ethereal solution of CH2(C0,Me),). The spectral properties are identical with those of the product of the resulting slurry was stirred at -78 "C for 10 min, the cooling bath reaction of 9+Tf0- and methyllithium, vide supra. Reaction of [q1-2-Bicyclo[3.2.1]oct-3-enylidene]di- was removed, and the reaction mixture was allowed to warm to ambient temperature. Filtration through a short alumina column, carbonyl(q5-cyclopentadienyl)iron(11) Triflate,9+TfO-, and concentration to dryness under vacuum, dissolution in pentane, Methanol. Preparation of [ql-2-(4-Methoxybicyclo[3.2.1]and chromatography on alumina using 3:l pentane/diethyl ether oct-2-enyl)]dicarbonyl(q5-cyclopentadienyl)iron(II),12. Cold to elute the slow-moving yellow band provided 0.095 g (53%) of 9+Tf0-, prepared from 0.107 g (0.341 mmol) of 4 and 5 and 0.2 14: IR (CH,Cl,) 2004,1952 (-C=O), 1732,1750 cm-' (C(=O)mL (0.23 g, 1.04 mmol) of trimethylsilyl triflate as described above OMe); 'H NMR (CD,Cl,) 6 4.94 (d, 1 H, CH=), 4.80 (s, 5 H, Cp was suspended in 10 mL of cold (-78 "C) diethyl ether and treated H's),3.70 ( d , 6 H,0CH3's),3.32(d, 1 H, CH(C02Me),),2.62-0.90 with 0.150 g of sodium bicarbonate. A cold (-78 "C), 1:lO (m, 9 H, +=CH's >CH,'s); 13C('HJNMR (CDCl,) 6 216.40 (methanol/diethyl ether mixture was added to the suspended 9' CEO'~), 169.21, 169.12 (the diastereotropic >CO=O's), 153.59 salts, and the resulting slurry was stirred at -78 "C for 30 min. (-C(C5H5(CO),Fe)=), 130.33 (CH=),85.43 (Cp), 53.45,49.33 and The cooling bath was removed, and the reaction mixture was 36.01 (+CH's), 52.77,52.68 (the enantiotopic OCH,'s), 33.61,31.94, allowed to warm slowly to room temperature. Filtration through 29.97 (>CH,'s); mass spectrum, m / e 386 [M - CO]", 358 [M a short column of alumina and concentration to dryness under 2CO]*+. Anal. Calcd for C2,Hz2Fe06:C, 57.97; H, 5.35. Found: vacuum provided a residue, which was taken up in a minimum C, 57.70; H, 5.12. volume of pentane and eluted as a pale yellow band from a column Reaction of [~'-2-Bicyclo[3.2.1]oct-3-enylidene]diof alumina with 1:l ether/pentane. The yield was 0.087 g (81%) carbonyl(v5-cyclopentadienyl)iron(11) Triflate,9+TfO-,and of methoxy C5H5(CO),Fe-vinyl 12: IR (CHzCl2)2004,1952 cm-' Vinyllithium. Preparation of [q1-2-(4-Vinylbicyclo[3.2.1](-CEO); 'H NMR (CDZC12) 6 5.41 (dd, 1 H, J ~ ( 3 ) 4 ( 4=) 3.99 Hz, oct-2-enyl)]dicarbony1(q5-cyclopentadienyl)iron(II), 15. Cold, JH(3)-H(5) = 1.39 Hz, =CH, which, when the doublet of doublets precipitated t3+CF3C0T,prepared as detailed previously from at 3.10 ppm is irradiated, is converted into a doublet, J = 1.39 0.150 g (0.477 mmol) of 4 and 5 and 0.3 mL (0.345 g, 1.55 mmol) Hz), 4.85 (s, 5 H, Cp H's), 3.29 (s, 3 H, OCH3), 3.10 (dd, 1 H, of trimethylsilyl triflate, was suspended in 25 mL of cold diethyl JH(~)-H(~) = 3.99 HZ, JH(4)+(5) = 2.37 HZ, >CHOMe, which when ether and treated with 0.95 mL of a 1.95 M solution of vinyllithium the doublet of doublets a t 5.41 ppm is irradiated is converted into in THF. The resulting mixture was stirred at -78 "C for 10 min, a doublet, J = 2.37 Hz), 2.55-0.88 (m, 8 H, 2 +CH's + 3 >CH,'s) and then the cold bath was removed slowly to allow the tem[PCM0DELzsb predicts J H ( 4 ) 4 ( 5 ) = 0.15 HZ, JH(3)-H(4) = 4.16 HZ for perature of the reaction mixture to rise gradually to room temthe exo isomer, JH(4)..H(5) = 1.87 Hz, &(3)44(4) = 3.09 Hz for the perature. After about 30 min the reaction mixture was filtered endo isomer]; 13C(1HJ NMR (CD2Cl,) 6 216.85, 216.60 (-CzO's), through a short column of alumina, and the resulting filtrate was 157.14 (-C(C5H5(CO),Fe)=), 132.24 (CH=), 85.76 (Cp), 83.42 concentrated to dryness at reduced pressure. The resulting residue (>CHOMe),55.55 (OCH3),53.99and 35.21 (+CH's),33.64,29.74 was dissolved in a minimum volume of pentane and chromatoand 25.28 (>CH,'s); mass spectrum, m / e 314 [MI'+, 286 [M graphed on a column of activity I1 alumina maintained a t -10 CO]'+, 258 [M - 2CO]'+. Anal. Calcd for Cl6HI8FeO3: C, 61.15; H, 5.78. Found: C, 60.98; H, 5.73. "C. The desired complex, 0.117 g (79%), eluted as a yellow band Reaction of [ql-2-Bicyclo[3.2.1]oct-3-enylidene]di- with a pentane/ether mixture: IR (CH,Cl,) 2005, 1950 cm-' (-CEO); 'H NMR (CDCl,) 6 5.82 (m, 1 H, CH=CHz), 5.05 (d, carbonyl(q5-cyclopentadienyl)iron(II)Triflate,9+TfO-, and 1 H, CH=CCH,'s); 13C('HJNMR (CDClJ 6 (p-Tolylthio)bicyclo[3.2.1]oct-2-enyl])dicarbonyl(~5-cyclo216.75 and 216.65 (-C=O's), 148.18(-C(C5H5(CO),Fe)=), 143.41, pentadienyl)iron(II), 13. Cold 9+Tf0-, prepared from 0.104 g (0.331 mmol) of 4 and 5 and 0.2 mL (1.00 mmol) of trimethylsilyl 133.95 (CH='s), 112.62 (CH=CH,), 85.47 (Cp C's), 54.67, 53.78, 38.14 (+CH's), 33.54, 32.80, 30.58 (XHpls); mass spectrum, m / e triflate as described above, was dissolved in 5 mL of cold (-78 "C) methylene chloride and treated with 0.07 g (0.479 mmol) of [MI'+, calcd for C1,H1,FeO2 310.0656, found, 310.0631. sodium p-methylthiophenoxide. The resulting mixture was stirred Reaction of [q1-2-Bicyclo[3.2.1]oct-2-enyl]dicarbonyl(q5cyclopentadienyl)iron(II), 10, and Trifluoroacetic Acid. briefly at -78 "C and then allowed to warm slowly to room temperature. Volatiles from the reaction mixture were removed a t Formation of [q1-2-Bicyclo[3.2.1]octylidene]dicarbonyl(~5cyclopentadienyl)iron(II), 16'CF3C02-. A solution of 10 mg reduced pressure, and the resulting residue was extracted with (0.035 mmol) of the starting material in -0.3 mL of methylene 9:l pentane/diethyl ether. The extract was filtered through a
-
+
New Route to Vinylmethylidenes chloride was placed in a 5-mm NMR tube under an inert atmosphere, and the solvent was slowly removed under reduced pressure so as to coat the lower 1-in. portion of the tube with a thin layer of the viscous yellow solute, 10. The tube was cooled in liquid nitrogen, and 0.5 mL of CDzCl2containing 25 mg (0.22 mmol) of trifluoroacetic acid was added. The cold tube containing the frozen reaction mixture was sealed under vacuum, inserted in the precooled (-89 "C) probe of the AM-300.13, and allowed to thaw and mix in the probe. The 13C('HJNMR spectrum, determined after 2 h, is essentially identical with that reported earlier3 for 16'BFL. The temperature of the probe was raised to -59 OC, and a second 13Cspectrum was recorded. It revealed the reaction mixture now to contain equal amounts of the exoand endo- (s2-3-bicyclo[ 3.2.11 octene)dicarbonyl(a5-cyclopentadienyl)iron(II)cations, 17+and 18+,respectively. The sample tube was then removed from the cold probe, allowed to warm to room temperature, and reinserted in the -59 "C probe, and the contents were again analyzed by 13C(lH}NMR. The only material present in solution was the exo-s-complex: 18+CF3CO2-,which was isolated by removing the solvent under vacuum and washing the residue with cold ether. Reaction of [ql-2-Bicyclo[3.2.1]oct-2-enyl]dicarbonyl(q5cyclopentadienyl)iron(II), 10, and Methyl Triflate. For23. A 0.4-mL (0.580 mation of 3-Methylbicyclo[3.2.l]oct-2-ene, g, 3.53 mmol) aliquot of freshly distilled methyl triflate was added to 3 mL of nitrogen-blanketed solution containing 0.190 g (0.669 mmol) of 10 in CHzC12 The resulting mixture was stirred at room temperature for 20 h, and the volatiles were removed a t reduced pressure (0.5mmHg, 60 "C), washed with 2 mL of water, and dried over NazS04. About 2 mL of freshly distilled hexanes was added, and the volume of the solution was reduced by slowly distilling the low-boiling volatiles (mostly CHzClz)through a wire-spiralpacked column a t atmospheric pressure. Gas chromatographic analysis of the residue on a 3 ft X 1/4 in. column packed with 20% Carbowax 20M on 100 mesh Chromosorb P at 120 "C indicated the presence of two olefins in the ratio of 1:lO. The minor hydrocarbon was identified as bicyclo[3.2.l]oct-2-ene by admixture with a known pure (98%) sample.41 The major component was (23)from the 13C identified as 3-methylbicyclo[3.2.l]oct-2-ene NMR [(CDC13)116 131.24 (C(Me)=),128.62 (CH=), 42.18, 35.73, 35.41 (>CH,'s), 35.02, 33.23 ( ~ C H ' S )30.39 , (>CHz), 22.93 (CH,)] and from the molecular ion in the mass spectrum (m/e [MI'+ calcd for C9H14122.20, found 122) as well as by comparison of the 'H NMR [(CDCl,) 6 5.54 (d, J = 7 Hz, 1 H, CH=), 2.89 (m, 3 H, >CHCH=C(Me)CH,), 1.81-1.39 (m, 10 H, +CH, >CH2's, CH3)] with that of known material.42 The GLPC yield of 23,determined by the addition of a known quantity of norbornene to the reaction mixture, was 94%. When the above reaction was carried out for 6 h at -78 "C then allowed to warm slowly to room temperature, the ratio of bicyclo[3.2.l]oct-2-ene to 23 in the reaction mixture was -2:l. To confirm the identity of 23, 3 mL of a solution of bicyclo[3.2.l]oct-2-eneand 23 in hexane, prepared a t room temperature as described above, was hydrogenated a t atmospheric pressure in the presence of a small amount of Pd/C. The mixture was filtered, dried over NaZSO4,and concentrated to about 1 mL by slow distillation through a wire-spiral-packed column a t atmospheric pressure. The resulting 3-methylbicyclo[3.2.l]octane(24) was separated and collected by preparative GLPC on the Carbowax 20M column (vide supra) and characterized spectroscopically: 'H NMR (CDC1,) 6 2.11 (br s, 2 H), 1.68-1.01 (m, 9 H), 0.95 (m, 2 H), 0.80 (d, J = 7.5 Hz, 3 H, CH,); 13C NMR (CDC1,) 6 41.99,39.36 (>CH,'s), 35.21 ( ~ C H ' S 29.19 ) , (>CHz), 25.49 (+CH), 22.56 (CH,). Although these 13Cchemical shifts are 0.3-0.5 ppm larger than those reported for exo-3-methylbicyclo[3.2.1]octane,23 we take this as conformation that 23 is, in fact, 3-methyl-
-
bicyclo[3.2.l]oct-2-ene. Reaction of [ql-2-(4-Methylbicyclo[3.2.1]oct-2-enyl)]dicarbonyl(~5-cyclopentadienyl)iron(II), 11, with Trifluoroacetic Acid. Formation of exo-4-Methylbicyclo[3.2.1]oct2-ene, 22. To a cold (-78 "C) solution of 0.072 g (0.242 mmol) (41) Organic Technology, Inc., Coshocton, OH. (42) Brun, P.; Waegell, B. Tetrahedron 1976,32, 1125. (43) Average of three separate determinations; the sample is apparently hygroscopic.
Organometallics, Vol. 9, No. 5, 1990 1507 of 11 in 10 mL of EGO was added 50 pL (0.565 mmol) of CF3SOsH. The mixture was stirred at -78 "C for 10 min, and the cold bath was removed. A yellow precipitate formed as the reaction mixture warmed to room temperature over a 30-min period. The supernatant solvent was removed by cannulation, and the precipitate was washed with 2 X 10 mL of ether and dried under vacuum to yield 0.082 g (76%) of a mixture whose l3C(lH}NMR spectrum (CD2C1,) indicated the presence of uncomplexed 4-methylbicyclo[3.2.l]oct-2-ene,22: 6 133.32 and 129.42 (-CH=CH-), 40.91,38.74,35.06,33.69,30.25 and 30.06 (3 X H s and 3 >CH,'s), 20.15 (CH,), and an unidentified C5H5(C0)zFederivative (6 209.74 (-CEO's), 84.59 (Cp)). In a second experiment, 0.2 mL (0.296 g, 2.60 mmol) of freshly distilled CF3S03Hwas added to a cold (-78 "C) solution of 0.095 g (0.319) mmol of 11 in 3 mL of CHzClz,and the mixture was stirred a t -78 "C for 30 min and then allowed to warm to room temperature over a 30-min period. The volatiles were removed under vacuum (0.5 mmHg, 25 "C), washed successively with 2-mL portions of saturated, aqueous NaHC03 and water, and then dried over anhydrous Na2SO4. The dried solution was diluted by the addition of -2 mL of freshly distilled hexanes, 0.018 g (0.167 mmol) of pure bicyclo[3.2.l]oct-2-ene was added as an internal reference, and the low-boiling components (mostly CHzClz)were removed by slow distillation through a wire-spiral-packed column a t atmospheric pressure. The resulting olefins were separated and collected by the preparative GLPC at 120 "C on a 3 ft X '/4 in. column packed with 20% Carbowax 20M on 100 mesh Chromosorb P. The yield of 4-methylbicyclo[3.2.l]oct-2-ene was 73% as calculated from the relative areas of the reference bicy(22)peaks. clo[3.2.l]oct-2-ene and 4-methylbicyclo[3.2.l]oct-2-ene It has the following spectra: 'H NMR (CDCl,) 6 5.81 (dddd, 1 H, J = 9.52, 6.60, 1.48, 1.49 Hz, >CHCH=CHCH(CH,)), 5.25 (ddd, 1H , J = 9.48, 3.76, 1.67 Hz, >CHCH=CHCH(CH,)), 2.31 (m, 1 H, >CHCH=CHCH(CH,)), 2.14-1.54 (m, 6 H, >CHz's), 1.43-1.34 (m, 1 H, >CHCH=CHCH(CH,)), 1.25-1.18 (m, 1 H, >CH), 0.97 (d, J = 7.1 Hz, >CH(CH,); mass spectrum, m/e (re1 intensity) [MI'+ 122 (32), 107 (25), 94 (22), 93 (loo), 91 (19) 79 ~ JH(l)-H(zl,5.93 Hz, &(3)-H(4) = 3.88 Hz, (95). P C M O D E L ~predicts: and JH(4)-H(5) = 1.04 Hz for the exo isomer; JH(l)-H(z) = 5.88 Hz, &(3)-H(4) = 3.01 Hz, and JH(4)-H(5) = 3.82 Hz for the endo isomer. The stereochemistry of the 4-methyl group of 22 was confirmed as exo by comparison of these spectra with those of authentic exo-4-methylbicyclo[3.2.1]oct-2-ene,'gviz: "'H NMR (CDC1,) 6 5.83 (dddd, 1 H, J = 10, 7.1, 1.5, 1.5 Hz), 5.27 (ddd, 1 H, J = 10, 4, 2 Hz), 2.3-2.4 (7, 1 H), 1.6-2.1 (m, 6 H), 1.4-1.5 (m, 1 H), 1.2-1.3 (m, 1 H), 1.00 (d, 3 H, J = 7 Hz); mass spectrum, m/e (re1 intensity) [MI'+ 122 (12), 107 (ll),94 (24), 93 (61), 91 (18), 81 (18), 80 (20), 79 (loo), 78 (12), 77 (27)" and endo-4-methylbicyclo[3.2.l]oct-2-ene: "'H NMR (CDC1,) 6 5.77 (dddd, 1 H, J = 10, 6, 2, 1 Hz), 5.16 (ddd, 1 H, J = 10, 2, 2 Hz), 2.5 (m, 1 H), 2.3 (m, 1 H), 2.1 (m, 1 H), 1.5-1.8 (m, 6 H), 0.92 (d, 3 H, J = 7.5 Hz); mass spectrum, m/e (re1intensity) [MI'+ 122 (40), 107 (27), 94 (32), 93 (loo), 91 (21), 81 (38), 80 (33), 79 (98), 78 (20), 77 (29)". Reaction of [ql-2-(exo-4-Methylbicyclo[3.2.1]oct-2enyl)]dicarbonyl(q5-cyclopentadienyl)iron(II), 11, and Trifluoroacetic Acid Followed by Variable-Temperature 13C(lH}NMR. A cold solution of 20 WLof CF3COZHin 0.6 mL of CDzClzunder Nz was syringed into a 5-mm NMR tube at -78 "C containing 0.027 g of 11. After the resulting mixture had been quickly mixed a t -78 "C, the tube was inserted into the precooled (-78 "C) probe of the NR-80 and the 13C(lHINMR spectrum of alkylidene 19+was recorded: 6 422.82 (>Fe+=CCH,'s), 20.19 (CH3). The probe temperature was slowly increased to -70 "C, and a second 13Cspectrum was recorded. Judging from the absence of resonances attributable to 19+and the presence of two distinct Cp resonances in the ratio of -2.4:l characteristic of an C5H5(CO)zFe(~2-olefin),"we presume the reaction mixture now primarily to contain an -2.4:l mixture of endo- and exo-s2-(exo4-methylbicyclo[3.2.l]oct-2-ene)dicarbonyl(~5hcyclopentadienyl)iron(II),20+ and 21+ respectively. 13C{'H)NMR 6 211.46 and 207.58 (-C=O's), 88.37 and 88.14 (q5-Cp C's), and (44) Laycock, D. E.; Baird, M. C. Inorg. Chim. Acta 1980, 42, 263.
1508
Organometallics 1990, 9, 1508-1510
severely overlapping resonances at 89.34 and 80.34,42.93,39.25, 38.64, 34.87, 33.67, 29.56, 23.11 (+CH's, >CH,'s and CH3's). The probe temperature was slowly raised to -50 "C, and a third 13C spectrum was recorded of the reaction mixture, viz., 8 210.57 and 208.30 (-C=O's), 88.58 (q5-Cp C's), 90.16 and 86.86 ($(CH=CH's)), 39.16 (2, +CH's), 38.25 (+CHI, 34.15, 32.11 and 28.52 (>CH,'s), 23.45 (CH,). We attribute these resonances to [ exo(?)-~2-(exo-4-methylbicyclo[3.2.l]oct-2-ene)dicarbonyl(~5cyclopentadienyl)iron(II)]t,21+. The NMR tube containing the reaction mixture was removed from the probe and maintained at 0 "C overnight, and a fourth spectrum identical with that of exo-4-methylbicyclo[3.2.1]oct-2-ene, 22,was recorded. Reaction of [ql-2-(4-Methoxybicyclo[3.2.1]oct-%-enyl)]dicarbonyl(q5-cyclopentadienyl)iron(II), 12, and Tetrafluoroboric Acid. Formation of [?'-2-Bicyclo[3.2.1]oct-3enylidene]dicarbonyl(q5-cyclopentadienyl)iron(11) Tetrafluoroborate,9+BF4-.A nitrogen-blanketed solution of 12 (0.035 E. 0.111 "01) in 0.6 mL of CDXL was cooled to -78 "C in a 5-mm NMR tube. To this cold solution was added 0.1 mL of HBF,.EhO, _I
the contents were mixed at -78 "C, the tube was placed in the precooled (-78 "C) probe of the NR-80, and the I3C{lH}NMR spectrum of the reaction mixture was determined. It is identical in all respects to that of 9+BF4-formed when an -3:2 mixture of 4 and 5 is protonated under similar conditions.
Acknowledgment. We thank Dr. Ron Garber a n d Helga Cohen for their help with the N M R coupling constant determinations. We are indebted t o the National Science Foundation for support of this work in the form of a research grant to the principal investigator, CHE8614928, a n d a grant, CHE-8904942, to the Department of Chemistry for t h e purchase of the 500-MHz N M R spectrometer. We are indebted to the NIH, which provided the Department under Instrumentation Grant, No. 1-510-RR02849, with funds for the purchase of the VG Analytical, Ltd., 70SQ high-resolution, double-focusing mass spectrometer and VG 11/ 250 data system used in this work.
Organolanthanide-Catalyzed Cyclodimerizations of Disubstituted Alkynes H. J. Heeres, A. Heeres, and J. H. Teuben" Groningen Center for Catalysis and Synthesis, Department of Chemistry, University of Groningen, Nijenborgh 16, 9747 AG Groningen, The Netherlands Received September 29, 7989
The lanthanide alkyls Cp2*LnCH(SiMe3)z(Ln = La, Ce) are efficient catalysts for the cyclodimerization of 2-alkynes MeCECR (R = Me, Et, n-Pr) to 1,2-disubstituted 3-alkylidenecyclobutenes.The first step in the reaction is a propargylic metalation of the a-methyl group, giving Cp*,LnCH2C=CR compounds and free CH2(SiMe3I2. Various lanthanide alkyls and hydrides are active alkene polymerization catalysts.'P2 In fact, Cp*2LnH (Ln = La, N d , S m , L U ) compounds ~ ~ appear t o be t h e most active ethylene polymerization catalysts known to date. T h e bis(pentamethylcyclopentadieny1)lanthanides are excellent models for the study of alkene polymerization. Mechanistic studies with this class of compounds have led to a better understanding of polymerization pathways and related reactions such as termination a n d chain transfer.2e In contrast, relatively little is known about organolanthanide-catalyzed alkyne oligomerization and polymerization. T h e reported literature deals mainly with acetylene polymerization by Ziegler-Natta type system^.^ Our interest in this area stems from the observation that CP*~Y-a n d Cp*2Sc-alkyl species are active catalysts for the selective dimerization of a-alkynes to 2,4-disubstituted (1) The following abbreviations are used in this article: Cp* = q5C6Me5 ring, Ln = lanthanide or group 3 element, Iw = line widths of NMR resonances at half-maximum. (2) (a) Watson, P. L. J . Am. Chem. SOC.1982,104, 337. (b) Watson, P. L.; Parshall, G.W. Acc. Chem. Res. 1985, 18,51. (c) Jeske, G.; Lauke, H.;Mauermann, H.; Swepston, P. N.; Schumann, H.; Marks, T. J. J. Am. Chem. SOC.1985, 107, 8091. (d) Evans, W. J. Adu. Organomet. Chem. 1985,24, 131. ( e )Parkin, G.; Bunel, E.; Burger, B. J.; Trimmer, M. S.; Van Asselt, A.; Bercaw, J. E. J. Mol. Catal. 1987, 41, 21. (3) (a) Shen, 2. Inorg. Chim. Acta 1987, 140, 7. (b) Bruzzone, M. In Fundamental and Technological Aspects of Organo-f-Element Chemistry; Marks, T. J., Fragala, J. L., Eds.; D. Reidel: Dordrecht, The Netherlands, 1985; p 387.
0276-7933/90/ 2309-15r18902.50/0
e n y n e ~ . In ~ this communication we report t h e reactivity of some well-defined lanthanide alkyls with various disubstituted alkynes. Reaction of c ~ * ~ L n c H ( S i M(Ln e ~ )=~ La, Ce) with a n excess of 2-butyne (benzene-&, 2-butyne/Cp*,LnCHratio 20:l) results in the catalytic formation of (1; a cyclic dimer: 1,2-dimethyl-3-ethylidenecyclobutene eq 1, characterized by M S a n d 'H and I3C N M R metho d ~ ) .T~h e reaction proceeds to completion in ca. 10 h at (4) (a) Den Haan, K. H.; de Boer, J. L.; Teuben, J. H.; Spek, A. L.; KojiC-ProdiE, B.; Hays, G. R.; Huis, R. Organometallics 1986,5, 1726. (b) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J . Am. Chem. SOC. 1987, 109, 203. (5) Cyclic dimer 1 was separated from the catalysts by vacuum transfer (25 "C, 0.01 mmHg) and obtained as a benzene-d, (or benzene) solution. Attempts to purify 1 by vacuum distillation (bp 38-40 "C, 24 mmHg) resulted in partial decomposition. Spectroscopic data for 1: 'H NMR (benzene-d6) 6 4.96 (4, 3JHH = 6.6 Hz, 1 H, =C(H)Me), 2.72 (s, 2 H, CH,), 1.66 (d, 3JHH = 6.6 Hz, 3 H, =C(H)Me), 1.61 (s, 3 H, Me), 1.51 (s, 3 H, Me); 13C NMR (benzene-d,) 6 141.3 (s), 140.4 (s), 139.2 (s), 102.5 (d, 'JCH = 153 Hz, =C(H)Me), 36.4 (t, 'JCH = 137 Hz, CHJ, 13.5 (4, 'JCH = 126 Hz,Me), 13.1 (4, lJCH= 126 Hz, Me), 9.1 (4, ' J C H= 126 Hz, Me); MS M'+ = m / e 108. 1 slowly decomposes in air and must be stored under nitrogen. NMR and GC methods and a successful computer simulation of 'H NMR spectra including all long-range proton-proton coupling constants suggest the formation of a single isomer. Attempts to determine the exact geometry of the ethylidene moiety by 'H NOE difference measurements were not successful. However, 2D NOESY spectra display a clear NOESY cross-peak between the ring CH, and the ethylidene methyl group and imply that the latter is pointing toward the ring CHz protons.
C 1990 American Chemical Society
